The rising popularity of wireless communication and the potential of a spectrum shortage motivated the United States Federal Communications Commission (FCC) to take steps towards releasing multiple new spectral bands and re-purposing some under-used spectral bands for dynamic spectrum sharing. Currently, actual utilization of the spectrum is sparse, with large swaths of spectrum in the gigahertz (GHz) range remaining underutilized. Dynamic sharing can more efficiently use these spectral bands by making these bands accessible to many different types of wireless services. For example, multiple ultra-wideband links can share the same wideband spectrum by using orthogonal time-hopping codes for time-modulated systems, or orthogonal pulses and orthogonal codes for fast-pulse-based systems.
There is also increasing demand for spectral sensing systems capable of identifying, locating, and responding to electromagnetic emissions found anywhere in extremely wide bandwidths (e.g., tens of GHz). Existing systems usually rely on sequential hopping from one relatively small portion of the spectrum (e.g., a “channel” or “band”) to another relatively small portion of the spectrum, typically covering only tens of MHz at a time. Therefore, only a small band in a much wider overall spectrum is monitored each time, making it easy to miss short lived signals (e.g., radar pulses or burst transmissions) in a given band of a wider swath of GHz spectrum.
In addition, on small platforms, it is desirable to reduce the size, weight, and power (SWAP) of the spectral sensing systems. Current systems typically use one or more instantaneous frequency measurement (IFM) receivers to detect signals and cue a more precise receiver or digital receiver array. Unfortunately, IFM receivers tend to be bulky and power consuming. For example, the Teledyne DR024-F2 IFM provides 2-18 GHz coverage with 3.93 MHz frequency resolution and consumes 18.5 Watts of power. Alternatives to IFMs include channelized receivers, direct digital receivers, and compressive receivers. Channelization is a relatively high SWAP alternative involving distribution of multiple local oscillator signals and large filter banks. Direct digital converters capable of converting more than about 2 GHz rely on interleaved analog-to-digital converters (ADCs) with low effective number of bits (ENOB) due to jitter. Compressive receivers provide very good performance, but still add SWAP to the overall system.